1. Field of the Invention
The present invention relates to a lens apparatus. Specifically, the invention relates to a lens apparatus comprising a focus lens to be moved forward or backward within an optical lens stroke by a driving force transmitted through a gear train from a drive source.
2. Description of Related Art
In the related art, there is known a lens apparatus comprising a lens which is allowed to move forward or backward by a driving force transmitted through a gear train from a drive source.
In this type of lens apparatus, generally, as a drive source, there is used a pulse motor (a stepping motor). When a driving force is transmitted through a gear train, a lens can be driven with higher resolution than that of the stepping motor (that is, with precision of a several μ unit).
However, since there exists a backlash in the gear train, when driving a lens, even if a lens drive amount (the number of pulses applied to the pulse motor) reaches a given value, the actual lens moving amount is smaller than the given value by an amount of play caused by the backlash of gears. Or, when the lens drive amount is a minute amount (for example, when the lens drive amount is smaller than the amount of play), the pulse motor is driven but the lens is not moved at all.
In view of this, in the related art, to solve such issues caused by the backlash in the gear train, for example, there are known a method for executing a given calculation or the like to set a backlash amount and thereby remove the backlash uniformly (Japanese patent No. 2773876), and a method in which data corresponding to an error caused by the backlash are previously prepared and, when the driving direction of the drive motor varies, a correction corresponding to the error is added to the drive amount of the drive motor (JP-B-5-58163).
However, since the method disclosed in Japanese patent No. 2773876 is a method in which a calculation or the like is executed using various parameters to thereby remove the backlash, under a given condition, the backlash can be removed but, out of the given condition, the backlash cannot be removed. Also, because the method disclosed in JP-B-5-58163 is a method for correcting the data on the drive amount of the drive motor, similarly, the backlash can be removed under a given condition but the backlash cannot be removed completely under the other remaining conditions.